1. Field of the Invention
This invention relates to the field of tools for the quality control of pipes and more particularly to tools for gauging external taper threads on pipes.
2. Prior Art
The American National Standards Institute, Inc. standards for pipe threads at Section 8, Paragraph No. 36, entitled "Gauging External Taper Threads", states that in gauging external taper threads an appropriate ring gauge is screwed handtight onto the pipe or external thread. The thread is within the permissable tolerance when the gauging face of the working ring gauge is not more than one turn, large or small, from being flush with the end of the thread. Thus, the practice in the past, has been to screw the ring gauge onto the end of the pipe, the tapered thread of which is being checked, and if the gauge can be screwed onto the pipe until the outer surface of the gauge is flush with the end of the pipe plus or minus one turn, the pipe is acceptable. However, experience has taught that, many times, there is a nick in one of the threads at a crucial point and the ring gauge may stop at that point if subjected only to the pressure that can be produced by the human hand. Many times such a nick is inconsequential as far as operation or use of the pipe is concerned and to avoid useless waste of pipe and high rejection rates it has been the practice to pound the pipe at its remote end on a cement floor to dislodge any dirt or to overcome any small nicks in the pipe threads being checked. That practice is provided for in Paragraph 38 of Section 8 of the American National Standards Institute, Inc.'s "Pipe Threads" standard which says, "In gauging pipe threads it is common practice to tap or wrap the part to assure proper seating of the gauge in or on the product thread. However, it is first necessary to clean both the gauge and the product threads so that they are free of chips, burrs, or other abrasives." Obviously, this is not a scientific method for gauging the acceptability of the pipes and their tapered threads. Attempts have been made to establish tapping and wrapping standards to attempt to achieve consistent quality control results. The quality control inspection instructions of the Southern California Gas Company, a very large user of pipes with external tapered threads, quotes from the American Society for testing materials Bulletin A733, "Steel Pipe Nipples" a definition of the wrapping technique used in the past, as follows: Swing the end of the fitting with the gauge attached through an arc of approximately four to six inches to allow the fitting to strike against the solid metal surface. This is used to eliminate any binding due to slight nicks or foreign matter in the thread". While this procedure may give some consistency to the results, it is still highly subjective in nature and cannot be expected to achieve a high level of consistency.
In a facility which manufactures or utilizes millions of feet of taper-threaded pipe a year, it is obviously desirable to maintain a high-quality of tapered thread at the same time as achieving a low reject rate on the pipes which are either manufactured or purchased to be utilized. Up until the date of my invention, no method for getting consistent quality control results has been available.
Therefore, it is an object of my invention to overcome the various disadvantages of prior art devices and methods, as set forth hereinbefore.
It is a further object of my invention to provide a tool which will provide to the tapping and wrapping step in the quality control of tapered threads on pipes the maximum degree of consistency while assuring maximum quality of the pipes which are found to be acceptable under the quality standards, utilizing my tool.